In the utility model patent CN 2614048Y assigned to the inventor of the present invention, there is disclosed an electric toothbrush having a bristle holder of the brush head mounted in a mounting portion and a groove machined on an outer wall of a side of the bristle holder to keep a restriction pin being inserted in the groove, and the other end of the restriction pin being fixed onto a top wall of a pot-shaped mounting portion of a hollow support tube. When the brush head of the electric toothbrush having the above structure is in mass production, the restriction pin fixed in the hollow support tube may become loosened due to the error in the production process, thereby the restriction pin fails to fix the bristle holder reliably, causing the bristle holder disengaging from the hollow support tube. If the user has used the brush head of the electric toothbrush for an extended period of time, the groove of the bristle holder and the restriction pin are seriously wear, or the fixation between the restriction pin and the hollow support tube become loosened, resulting in the bristle holder disengaging from the hollow support tube. Some serious consequences will follow, for example, the user may swallow the bristle holder into his/her trachea, stomach, etc., if the bristle holder disengages from the hollow support tube during movement. What's even worse, the bristle holder may be stuck in the throat such that the user may have problem in breathing.
Several types of brush heads of the electric toothbrush on the market have been recalled for many times since the user is injured by the disengagement of the bristle holder from the product. Another patent application (publication No. CN 103784207A) of the inventor of the invention discloses a personal electric cleaning tool having a head connected with a carrier that carries cleaning element. The carrier includes a connecting part that can be accommodated within the head and a securing part for securing the cleaning element. The securing part extends from the connecting part along its first rotational axis and simultaneously extends in the radial direction perpendicular to the first rotational axis. The connecting part is provided with a pair of opposite arc-shaped grooves circumferentially on its external surface. Correspondingly, the head is provided with a pair of opposite stop pins in radial direction, wherein one end of each of the stop pins is fixed onto the head, while the other end protrudes to the interior of the head so as to be accommodated and engaged with the arc-shaped grooves respectively. Thereby, when the carrier rotates around the first rotational axis, the stop pins are positioned within and engaged with the corresponding arc-shaped grooves all the time, such that the disengaging of the carrier from the head is limited.